The OVA Memories in the Rain is an alternate retelling of episodes 8-9 and can be watched first or after episode 9. Soul Society Arcs (Episodes 21-63)
This is the longest saga. It is interrupted by several filler arcs (noted below) that can be skipped to maintain story pacing.
Widely considered the series' peak. Watch every episode here, though some guides suggest skipping episode 33 and 50 as they are standalone filler.
Bleach episode 5, "," is part of the initial Substitute Soul Reaper arc and focuses on Ichigo and Rukia dealing with the Hollow known as Shrieker.